Field of the Invention
The present invention relates to an imprint apparatus, an illumination optical system, and an article manufacturing method.
Description of the Related Art
As demand for micropatterning of a semiconductor device, a MEMS, or the like increases, a microfabrication technique of molding an uncured resin on a substrate using a mold to form a resin pattern on the substrate has received attention, in addition to a conventional photolithography technique. This technique is also called an imprint technique and can form a fine structure of several nm order on the substrate. A photo-curing method is one example of the imprint technique. In an imprint apparatus which adopts this photo-curing method, first, an ultraviolet-curing resin is applied to a shot as an imprint region on the substrate. Next, the uncured resin is molded using the mold. Then, the resin is irradiated with an ultraviolet beam and cured, and the mold is released from the cured resin, thereby forming the resin pattern on the substrate. It can be said that the imprint apparatus is a semiconductor manufacturing apparatus capable of achieving a lower cost as compared with a conventional optical stepper, optical scanner, or EUV exposure apparatus because it does not need a projection optical system which reduces and projects a reticle pattern on the substrate.
The substrate to undergo an imprint process may be enlarged or reduced, and the shape (or the size) of the pattern may change in the biaxial direction perpendicular to each other in a plane after a heating treatment in a deposition step such as sputtering in a series of device manufacturing processes. Therefore, the imprint apparatus needs to match the shape of a substrate-side pattern that has been formed on the substrate beforehand with the shape of a die-side pattern portion that has been formed on the mold when bringing the mold and the resin on the substrate into contact with each other.
Japanese Patent Laid-Open No. 2013-89663 describes an imprint apparatus which includes a heating mechanism for heating a substrate-side pattern in order to match the shape of the substrate-side pattern with the shape of a mold pattern portion. The heating mechanism described in Japanese Patent Laid-Open No. 2013-89663 includes a liquid crystal element array or a digital mirror device as a spatial light modulation device which forms a light amount distribution in the planar region of the substrate-side pattern.
In the invention described in Japanese Patent Laid-Open No. 2013-89663, an illuminance is controlled by using, as the spatial light modulation device, digital micromirror devices (DMDs) positioned in a matrix or liquid crystal elements positioned in the matrix to tilt an arbitrary micromirror by a predetermined angle. Although not described in the invention described in Japanese Patent Laid-Open No. 2013-89663, a microlens array (MLA) or the like is generally used such that light which irradiates the DMDs has a top flat and uniform intensity distribution. The shot size of a wafer typically has a rectangular shape of 33×26 mm. In consideration of using a lower power light source to reduce the cost of the light source, the efficiency of an optical system needs to be increased. Therefore, the illumination width of illumination light to the DMDs is required to have a similar figure to the shot size. However, Japanese Patent Laid-Open No. 2013-89663 does not disclose that the illumination width of illumination light to the DMDs has the similar figure to the shot size.
A method which is performed as a conventional technique of changing the shape of illumination light to a DMD from a square to a rectangle will be described with reference to FIG. 4. In FIG. 4, letting P be the lens array pitch of an MLA, f1 be the composite focal length of two lenses of the MLA, and f2 be the each focal length of a Fourier transform lens, an illumination width D for a DMD plane can be obtained from D=P×(f2/f1). From this equation, the MLA pitch P or the focal length of the MLA needs to be changed between the X direction and the Y direction such that illumination light to the DMD has a similar figure to a shot size. In this case, the cost of an optical system increases because of the need to produce a special MLA. On the other hand, if the efficiency of the optical system is decreased as a result of keeping the cost of the optical system low, a higher output light source becomes required and the cost of the light source increases. As described above, if a method of improving an overlay accuracy by thermally deforming the pattern is applied to the imprint apparatus, the cost increases. This is contrary to a cost reduction which is one of advantages of the imprint apparatus.